1. FIELD OF THE INVENTION
The present invention relates to agricultural spreaders of the broadcast type and, more particularly, to dual rotary impeller broadcast spreaders for the distribution of particulate or granular materials such as fertilizers, pesticides, seeds and the like.
2. DESCRIPTION OF THE INVENTION
Various dual rotary impeller broadcast spreaders have been disclosed heretofore. For example, U.S. Pat. Nos. 1,769,302; 2,474,065; 2,537,913; 2,958,530; 2,989,314; 3,085,807 and 3,109,657 show versions of such devices which employ two rotating impellers to broadcast or discharge particulate material deposited on the impellers beyond the spreader to cover a region wider than the dimensions of the spreader. In these devices, one impeller is positioned on the left-hand side of the spreader as viewed from the rear of the device facing forwardly in the direction of advance of the spreader and the other impeller is positioned on the right-hand side of the spreader viewed in a similar manner. These left and right-hand impellers are positioned in coplanar, adjacent configurations. In the previously disclosed devices, the spreader is pulled or driven in a forward direction with the impellers rotating such that the particulate material is discharged in a rearwardly direction. Thus, in each of these prior devices, the direction of discharge of the particulate material is directly opposite to the direction of advance of the spreader. Accordingly, the relative rotational correspondence of the two impellers is different depending on whether the impeller rotation is viewed in the direction of spreader advance or in the direction of material discharge.
Specifically, when the left-hand impeller (as viewed from the rear of the device facing in the direction of spreader advance) rotates in a clockwise direction and the companion right-hand impeller rotates in a counterclockwise direction, the resulting rotational correspondence of the impellers (in the direction of material discharge) is away from one another. Such impeller rotation pattern results in the ejection of the particulates from the impeller surfaces in a non-uniform pattern across the intended coverage path or swath. Furthermore, when the impellers rotate in such manner, the coverage pattern is typically skewed to both sides of the spreader path. Accordingly, devices constructed with double rotary impellers demonstrating rotational correspondence wherein the impellers rotate away from one another, have been found to be incapable of providing an optimal spread or distribution pattern in a device of acceptable, commercially practical size.
Alternatively, when the left-hand impeller of the prior devices rotates in a counterclockwise direction as viewed from the rear of the device facing in the direction of spreader advance and the companion right-hand impeller rotates in a clockwise direction, the resulting rotational correspondence of the impellers (in the direction of material discharge) is toward one another. In prior devices exhibiting such rotational correspondence of the impellers, it has been necessary to construct the device in a manner such that the material drop position on the impeller is located at a position adjacent the forward lead edge of the spreader so that the particulate material will be discharged rearwardly of the spreader relative to the direction of advance of the device. Thus, the particular material drop position on the impellers of these prior devices is an essential feature thereof in order to achieve the desired material distribution or spread pattern. If the particulates are deposited on the impellers at different locations, the resulting coverage pattern achieved would not be optimal and, indeed, the material could be thrown into the operating mechanism of the device rather than being expelled outwardly therefrom.
Thus, it has been an inherent problem in the construction of dual rotary impeller spreader devices to achieve an optimal spread pattern of broadcast particulate material utilizing a controlled distribution pattern from each of the individual impellers so that an additive spreading effect is achieved from the two rotating members.
Further problems have been encountered in regard to the construction of dual rotary impeller broadcast spreaders concerning the arrangement of the material drop position on the impeller. In view of the fact that each of the prior devices has been constructed for movement in a forward direction with the discharge of material being in an opposite, rearward direction, it has been necessary to provide for the depositing of material onto the impellers at a position incapable of providing an optimal coverage or spread pattern in a forward spreader advance direction.